1. FIELD OF THE INVENTION
This invention relates to an interface converter that converts a first serial interface (hereinafter referred to as "1st I/F") which transfers digital binary serial data, control signals, timing signals, and other data between one electronic device and another electronic device in data transmission, into a second serial interface (hereinafter referred to as "2nd I/F") with specifications different from the 1st I/F. The term "specification" as used herein means electrical, physical, and logical specifications.
2. DESCRIPTION OF RELATED ART
The RS-232-C prescribed by the U.S. EIA, is known widely as a standardized interface. The RS-232-C is suitable for data transfer of a speed in the range of from 0 to 20 kilo-baud and of a distance between two points of less than 15 meters. On the other hand, the RS-422-A, also prescribed by U.S. EIA, is also known as a standardized interface for data communications, able to transmit data at higher speeds and over longer distances as compared with the RS-232-C. Namely the RS-422-A has a data transfer speed of 100 kilo-baud for 1.2 km and enables transfer at even 10 mega-baud over short distances. Therefore in recent years, interface converters which enable electronic devices equipped with an RS-232-C I/F to match the specifications of the RS-422-A have been put on the market.
As shown in FIG. 25, a conventional interface converter 1 has a connector 2 of the RS-232-C I/F on one side and a connector 3 of an RS-422-A I/F on the opposite side. The connector 2 of the converter 1 is connected to a connector 6 of the RS-232-C I/F of an electronic device 5 through a cable 4 of the RS-232-C I/F. The connector 6 is attached to an interface board 7 of the RS-232-C I/F installed in the device 5.
The conventional converter 1 converts therein the RS-232-C I/F into the RS-422-A I/F to which the single connector 3 is connected. When connecting the device 5 to a plurality of other devices 15, 25, . . . , the connector 3 is connected to a terminal unit 18 for the next interface converter 11 through a cable 3a, a terminal unit 8, and a cable 9, and then the terminal unit 18 is connected to a connector 13 through a cable 13a. By making the unit 18 a repeater, the unit 18 is connected to a terminal unit 28 for the next interface converter 21 through a cable 19. A repetition of such connection enables connection of a plurality of devices through a plurality of interface converters and to constitute a circuit in a multidrop style.
The above converter 1 (11, 21, . . . also same) is constructed using the cable 4 of the RS-232-C I/F and the cable 3a of the RS-422-A I/F. Therefore there are problems that the connection between the converter 1 and the device 5 becomes large-scale and requires practically a very big space.
The conventional multidrop style circuit connection of the RS-422-A I/F could only use repeaters, such as terminal units 8, 18, 28, . . . as mentioned above, once in order to avoid using a T-branched cable, which limits the number of devices connected. Circuit connection with these units 8, 18, 28, . . . is, however, complicated. Consequently, there is another problem that it is not easy to construct the circuits of the RS-422-A I/F.